JP 2005-89441 A discloses a method for producing a derivative of nucleotides called an oxazaphospholidine method. However, the isolate yield of the monomers is low and the method requires special capping agents that are not commercially available. Further obtained monomers are chemically unstable. Furthermore, the isolate yields of oligonucleotide derivatives are not high. It is thought that the low yield of oligonucleotide derivatives is caused by the degradation reactions under the de-protection steps.
WO2010/064146 pamphlet discloses a method for producing a derivative of nucleotides. The method disclosed therein requires special capping agents that are not commercially available. Furthermore, the isolate yields of oligonucleotide derivatives are not high. The low yield is thought to be caused by the degradation reactions under the de-protection steps. This tendency becomes strongly apparent when the length of oligonucleotide derivatives becomes long.
WO2012/039448 pamphlet discloses Asymmetric auxiliary group which is used to produce stereocontrolled phosphorus atom-modified oligonucleotide derivatives.